Modeling Titanium Aluminide Based Alloys from Atomic to Lamellar Scales

Titanium aluminide-based alloys have found use in the aerospace industry in applications such as low pressure turbine blades due to their light weight and high temperature properties. It is necessary to develop a deep understanding of the structure-property correlations of these materials in order to understand how to engineer their mechanical properties. To this end, we have used models at multiple length scales to explore the relationship between temperature, microstructure, and mechanical properties. At the atomic scale, we performed a critical evaluation of existing empirical potentials and found that potentials based on the Embedded Atom Method and the Modified Embedded Atom method were capable of replicating most (but not all) mechanical properties as compared to DFT and experiment. For example, all existing models tend to overestimate the thermal expansion coefficients in the α2-Ti3Al structure. At the lamellar structure, we developed a crystal plasticity model that explicitly accounts for the alternating lamellae of γ-TiAl and α2-Ti3Al. By phenomenologically including experimentally observed trends such as the temperature-dependent yield stress anomaly and deviations from Hall-Petch behavior, we were able to establish relationships between orientation dependent deformation, structural length scales such as lamellae thickness, and stress state.